The present invention relates to a ventilation system for a crankcase of an internal combustion engine.
In the crankcase of an internal combustion engine, blow-by gases arise which for reasons of environmental protection are usually led to the intake section of the combustion engine. The pressure difference between the crankcase and the intake section is used in order to return the blow-by gases from the crankcase into the intake section.
A ventilation system for a crankcase for the transport of blow-by gases thus usually comprises a ventilation line which reaches from the crankcase to the intake section. Further, an air-oil-separator is arranged in the ventilation line in order to separate oil and oil mist contained in the blow-by gases from these blow-by gases. The air-oil separator and/or the return line may comprise a tank for separated oil. The separated oil is then returned from this air-oil separator to the crankcase. It shall be stressed that in the context of this invention, ventilation does not mean the provision of fresh air to the crankcase but the transport of blow-by gases from the crankcase to the intake section.
What is problematic with this is that the return of the separated oil into the crankcase has to be effected against a pressure difference between the air-oil separator and the crankcase. To this end, different solutions have been developed in the state of the art. On the one hand, it is possible to integrate a siphon into the oil return line reaching from the air-oil separator to the crankcase which when sufficiently highly filled with separated oil is able to overcome the pressure difference relative to the crankcase. It is however disadvantageous that with the space available, a siphon of only very limited height can be installed so that only small pressure differences can be surmounted. This means that the return of the oil from the air-oil separator to the crankcase through the siphon can only be realized if favorable pressure conditions are given, meaning a small pressure difference between the air-oil separator and the crankcase. Thus only with particular operating conditions of the combustion engine, a sufficient return of the oil from the air-oil separator to the crankcase is ascertained. With this solution, it is required to arrange the air-oil separator ahead of the pressure control, as otherwise under partial-load operation, the pressure conditions required for the oil return do never occur. This in turn is related to the disadvantage that the pressure control only takes place in relation to the crankcase pressure plus the pressure difference at the air-oil separator. Variable blow-by volumes cause very different pressure differences at the air-oil-separator. As the design of the air-oil separator and of the pressure control system has to be realized with respect to the worst case, under average operation conditions, only a smaller pressure difference than the one actually available can be used for the air-oil separation so that an unnecessary high percentage of oil remains in the blow-by gas. While an inverted arrangement of air-oil separator and pressure-control valve would increase the pressure difference available for the air-oil separation for most of the situations, it would at the same time increase the pressure difference between the separated oil and the crankcase pressure, so that the return of the separated oil was even deteriorated.
A further alternative consists in collecting the separated oil in a tank. This tank, preferably at its bottom wall, is connected with the crankcase via a draining line or return line, with a return valve being installed in the draining line or return line as tank-outlet valve. With this solution, the separated oil is collected in the tank as long as the effective pressure resulting from the pressure difference between the crankcase and the intake section and the preload of the valve is higher than the oil pressure in the tank, thus the pressure resulting from the collected oil. The collected oil is then returned into the crankcase, for instance when the engine is shut down. In order to achieve good draining performance and a complete emptying, the tank closure valve shows no or only a small preload, which on the other hand means that due to insufficient sealing, untreated blow-by gas may reach the intake section. In order to allow for long periods of operation, it is further required to provide for a sufficient tank volume, which has a negative impact on the demand in installation space.
FIG. 1 shows an internal combustion engine in a schematic cross-section. The combustion engine 2 with crankcase 3 comprises a intake section 4 in which an air filter 6, a supercharging device 5, a throttle flap 7 and an air inlet valve 8 are arranged one after the other in the flow direction of the entering air. In the state of the art, turbo chargers and compressors are known as supercharging devices.
Between the crankcase 3 and the intake section 4, a ventilation line 100 is arranged, which comprises the sections 100a to 100e. The blow-by gas leaves the crankcase 3 through the section 100c of the ventilation line and flows towards an air-oil separator 11a, from which the purified gas flows further through section 100d to a pressure control valve 11b, which is followed by section 100e of the ventilation line. Thus, an air-oil separator 11a and a pressure-control valve 11b are arranged in this sequence in the ventilation line. Behind the pressure control valve 11b, the ventilation line 100 in its section 100e branches off, so that the section 100e in total shows a T-shape. One of its branches together with section 100a of the ventilation line constitutes the ventilation line for partial-load operation, while the other one of its branches together with section 100b of the ventilation line forms a ventilation line for full-load operation. Both in the ventilation line for partial-load operation and the ventilation line for full-load operation, return valves 12 (in the ventilation line for partial load) and 18 (in the ventilation line for full load), respectively, form the transition between section 100e and sections 100a and 100b, respectively.
During partial-load operation of the combustion engine 2, downstream the return valve 12, thus in section 100a of the ventilation line, a vacuum compared to the pressure in the crankcase 3 is given. Therefore, the return valve 12 in the ventilation line for partial load is open and the blow-by gases are sucked via the sections 100c, 100d, one branch of 100e, 100a of the ventilation line 100 via the intake section 4 into the engine 2.
During full-load operation, the compression device 5 causes a compression of the combustion air so that now downstream of the compression device 5 including section 100a of the ventilation line, a higher pressure compared to the pressure in the crankcase 3 is given. This causes a closure of the return valve 12 in the ventilation line 100a for partial load. The crankcase gases are now ventilated via the sections 100c, 100d, one branch of 100e, and 100b of the ventilation line into the intake section 4 in its segment upstream of the compressor 5, thus for instance between the air filter 6 and the compressor 5.
This way, a ventilation of the crankcase is guaranteed both during partial-load operation as well as during full-load operation. Starting at the air-oil separator 11a, an oil-return line with a siphon 13a is arranged between the air-oil separator 11a and the crankcase 3, via which separated oil is returned into the crankcase 3. As described beforehand, it is required to design this oil-return line 13 and especially the siphon 13a in such a way that at least under favorable pressure conditions, the separated oil is returned into the crankcase surmounting the higher pressure given in the crankcase. At the same time, the oil forms a barrier for blow-by gases.